1. Field of the Invention:
The present invention relates to a composite magnetic head capable of high density recording and high density reproduction, and a method for manufacturing such a composite magnetic head.
2. Description of the Prior Art:
In a recording system employing a disc-shaped magnetic recording medium, such as a magnetic disc, having circumferential recording tracks, the leakage of magnetic flux, namely, so-called cross-feed recording on the adjacent tracks during the recording operation and so-called cross-talk between the adjacent tracks during the reproducing operation, is liable to occur when the tracks are formed with small intervals therebetween in order to increase the recording density of the magnetic recording medium.
A composite magnetic head as illustrated in FIGS. 3 and 4 has been proposed so far to solve the problem of cross talk. This composite magnetic head has a basic function to form silent guard bands each having a guard band width Te on opposite sides of a recording track having a recording with Tw recorded by a recording/reproducing gap 10 by sweeping the outside of the recording track with a pair of erasing gaps 20. Provision of the guard bands having the guard band width Te on the opposite sides of the recording track having the recording track width Tw obviates cross-feed and cross talk between the adjacent tracks, even if the tracks are formed at a small intervals.
This conventional composite magnetic gap is formed by combining a recording/reproducing magnetic core 11 and an erasing magnetic core 21 with a nonmagnetic layer 29, such as a ceramic layer or a galss layer. The recording/reproducing magnetic core 11 is formed by joining an I-shaped half core 12 and a C-shaped half core 13 with the recording/reproducing gap 10 therebetween. The erasing magnetic core 21 is formed by joining an I-shaped half core 22 and a C-shaped half core 23 with the erasing gaps 20 therebetween. The recording/reproducing gap 10 and the erasing gaps 20 are packed with nonmagnetic materials 14 and 24, such as a glass having a high melting point, respectively.
Grooves 15 are formed on opposite ends of the recording/reproducing gap 10 in the opposite lateral sides of the recording/reproducing magnetic core 11 so as to extend over both the half cores 12 and 13. The grooves define the track width Tw and are filled with a nonmagnetic material 16, such as glass.
A hole 25 having a lateral width Ew is formed at the middle of the erasing gap 20 so as to extend over the half cores 22 and 23. The hole 25 defines the erasing track width Te and is filled with a nonmagnetic material 26. The lateral width Ew of the hole 25 is practically the same or less than the recording/reproducing track width Tw. The longitudinal width Gl, namely, the width along the longitudinal direction of the track, of the hole 25 is twenty times that of the gap size of the erasing gap 20 or greater in order to ensure erasing effect.
Coils 17 and 27 are wound on the respective C-shaped half cores 13 and 23 of the recording/reproducing magnetic core 11 and the erasing magnetic core 21, respectively.
This conventional composite magnetic head, however, requires complicated manufacturing processes, needs high manufacturing cost and has difficulty in being manufactured in high accuracy. In manufacturing the composite magnetic head, the half cores 12 and 13 of the recording/reproducing magnetic core 11 and the half cores 22 and 23 of the erasing magnetic core 21 are formed by cutting blocks as indicated by alternate long and two short dashes lines in FIG. 3. Since the grooves 15 and the hole 25 are formed in both the half cores 12 and 13, and in both the half cores 22 and 23, respectively, the grooves 15 and the hole 25 unavoidably need to be formed before the half cores 12 and 13, and the half cores 22 and 23 are joined together. However, when the half cores 12 and 13 and the half cores 22 and 23 are joined together, respectively, after forming the grooves 15 and the hole 25, it is possible that the grooves 15 and the hole 25 deviate from the respective correct positions in joining the half cores. It is apparent that high density recording is impossible unless the grooves 15 and the hole 25 are formed at the respective correct positions. Accordingly, accurate positioning of the grooves 15 and the hole 25 requires difficult work and complicated manufacturing processes, reduces the yield and increases the manufacturing cost.
In order to enable high density recording on a rotary recording medium, it is desirable to reduce the interval l between the recording/reproducing gap 10 and the erasing gap 20 to the least possible value. However, in the conventional composite magnetic head, since the grooves 15 and the hole 25 need to be formed over the entire length of the half cores 12 and 22, respectively, the half cores 12 and 22 need to have a sufficient thickness, and hence it is difficult to reduce the interval l to a satisfactorily small value.